Process for producing a composite alkali metal oxide

ABSTRACT

There is provided a composite oxide represented by the formula 
     
         iR.sub.2 O.jAl.sub.2 O.sub.3.kTiO.sub.2.mSiO.sub.2.nH.sub.2 O 
    
     wherein R denotes an alkali metal, i is 0.3 to 1, k is 0 to 0.9, j+k=1, m is 7 to 70 and n is 0.2 to 0.4, said composite oxide being amorphous, and its cumulative specific pore volume of pores having a pore radius of 10 4  A or less being 2.0 to 3.0 cc/g. This composite oxide can be produced by a process which comprises a first reaction step of adding an acid aqueous solution capable of forming a silicate by reaction with an alkali silicate to 7 to 10% by weight, calculated as silica, of an alkali silicate aqueous solution in the presence of a salt at 10 to 45° C. such that a neutralization ratio becomes 20 to 40%, and a second reaction step of heating the reaction solution obtained in the above reaction at temperature of 90° C. to a boiling point of the reaction solution and adding thereto an acid aqueous solution capable of forming a silicate by reaction with an alkali silicate such that pH of the reaction solution becomes 3 to 5.

This application is a division of U.S. application Ser. No. 07/922,837,filed Jul. 31, 1992, now U.S. Pat. No. 5,262,142.

Paper-making fillers are used by incorporating same in a starting pulpslurry at the time of paper-making. Such paper-making fillers areprincipally used to improve whiteness of a paper, improve opacity of thepaper, prevent ink printed on the surface from reaching a reverse side,i.e., prevent so-called opacity of the paper after printing, and soforth.

As the paper-making filler, a silica containing composite oxide havinggood absorption characteristics of ink is known. For example, JapanesePatent Publication Nos. 7715/1955, 3408/1964 and 13449/1970 disclose acomposite oxide comprising aluminum silicate, titanium silicate,zirconium silicate, etc. as a paper-making filler. Of these paper-makingfillers, especially aluminum silicate which is a composite oxide ofalumina and silica can preferably be used because fillability in a paperis good owing to adaptability to a starting pulp caused by aluminacontained therein.

However, in case of adding such an aluminum silicate to a paper as apaper-making filler, there has been a problem that when the basic weightof paper reaches less than 43 g/m² in order to make the paperlight-weight, an effect of preventing opacity of the paper afterprinting becomes poor.

The present inventors have made assiduous investigations over a relationof properties of a filler and an effect of preventing opacity afterprinting of the paper obtained by addition of the filler.

As a result, it has been discovered that a specific pore sizedistribution of the filler and its pore volume are important in theeffect of preventing opacity of the paper after printing. That is,findings have been acquired that absorption of ink in a composite oxideis greatly influenced by a cumulative specific pore volume (hereinaftersimply referred to at times as a "pore volume") of pores having a poreradius of 10⁴ Å or less and that when the pore volume is small, thepaper using the composite oxide does not exhibit the effect ofpreventing opacity of the paper after printing.

On the basis of these findings, aluminum silicate proposed so far as apaper-making filler has been pore radius of 10⁴ Å or less is at most 1.9cc/g, and a paper using such a composite oxide is, as stated before,insufficient in effect of preventing opacity of the paper afterprinting.

Accordingly, it is an object of this invention to provide a compositeoxide which is higher in pore volume of pores having a pore radius of10⁴ Å or less than the conventional composite oxides and which cansuitably be used as a paper-making filler excellent in absorbability ofink and effect of preventing opacity of the paper after printing even ifits amount added to the paper is small.

Further, this invention is to provide a process for producing thecomposite oxide with good efficiency.

The other objects of this invention will be made clear from theforegoing explanation.

The composite oxide provided by this invention is represented by formula(A)

    iR.sub.2 O.jAl.sub.2 O.sub.3.kTiO.sub.2.nH.sub.2 O . . .   (A)

wherein R denotes an alkali metal, i is 0.3 to 1, k is 0 to 0.9, j+k=1,.m is 7 to 70 and n is 0.2 to 0.4, said composite oxide being amorphous,and its cumulative specific pore volume of pores having a pore radius of10⁴ Å or less being 2.0 to 3.0 cc/g.

The composite oxide of this invention can be formed as follows.

(1) Chemical composition of formula (A)

Confirmation can be conducted by determining the amounts of R₂ O, Al₂O₃, TiO₂ and SiO₂ by a fluorescent X-ray method and calculating a molarratio of the respective oxides.

(2) Crystal structure

That the composite compound is amorphous can be confirmed by X-raydiffraction thereof.

(3) Cumulative specific pore volume of pores having a specific poreradius

The composite compound dispersed in water is filtered, and the obtainedcake is dried at 105° C. A pore volume of the dried cake is measured bya mercury porosimeter. A cumulative graph showing a relationship of thepore volume to the pore radius is prepared, and the pore volume in thespecific pore radius can be found on the basis of the cumulative graph.

The composite oxide of this invention, as represented by the formula,makes silica and alumina essential oxide components, and can contain analkali metal oxide and/or titania at a specific ratio. Especially acomposite oxide of the formula wherein i is 0.5 to 1, k is 0 to 0.9,j+k=l, m is 15 to 65 and n is 0.2 to 0.4 is preferable as a paper-makingfiller because the effect of preventing opacity of the paper afterprinting is excellent. The composite oxide containing titania canincrease characteristics such as whiteness and opacity of paper inaddition to the effect of preventing opacity of the paper afterprinting.

Since the composite oxide of this invention has the pore volume of poreshaving the specific pore radius within the specific range, it exhibitsthe excellent effect as the paper-making filler. That is, because thecumulative specific pore volume of pores having the pore radius of 10⁴ Åor less is 2.0 to 3.0 cc/g, not only the amount of ink absorbed islarge, but also a very good effect of preventing opacity of the paperafter printing is exhibited which has been hardly achieved with theconventional paper-making filler made of aluminum silicate.

The composite oxide of this invention has the specific pore volume aswell as a characteristic pore distribution that the cumulative specificpore volume of pores having a pore radius of 5×104 % or less is 2.4 to4.0 cc/g, that of pores having a pore radius of 3000 to 4 ×10⁴ Å is 0.6cc/g or more, especially 0.8-1.6 cc/g, and that of pores having a poreradius of 100 to 1000 Å is 0.6 cc/g or more, especially 0.7 to 1.6 cc/g.As the pore volumes of pores having the specific pore radii are withinthe above ranges, the excellent effect of preventing opacity of thepaper after printing can be shown when the composite oxide is used as apaper-making filler.

Namely, a printing ink for paper is composed of a pigment and a vehicle.From the experiments of the present inventors, it has been found thatthere is a difference in pore radius of fillers that absorb and adsorbthe pigment and the vehicle, namely the pigment is absorbed and adsorbedin pores having a pore radius of 3000 to 4×10⁴ Å, and the vehicle inpores having a pore radius of 100 to 1000 Å, respectively.

Since the pore volumes occupied by the pores having these specific poreradii are quite large as noted above, the composite oxide of thisinvention exhibits the excellent effect of preventing opacity of thepaper after printing as a paper-making filler.

Meanwhile, regarding aluminum silicate, there has been almost noliterature that focuses on the pore radius as noted above. Besides,aluminum silicate so far known as a paper-making filler is quite low inpore volume of pores having a pore radius of 10³⁴ Å or less compared tothe composite oxide of this invention; pore volumes of pores having poreradii or 10⁴ or less, 3000 to 4×10⁴ Å and 100 to 1000 Å are also smallcompared to the composite oxide of this invention. For example, in caseof aluminum silicate commercially available as a paper-making filler, asshown in Comparative Examples to be described later, a pore volume ofpores having a pore radius of 10⁴ Å or less is at most 1.9 cc/g, that ofmost 2.3 cc/g, that of pores having a pore radius of 3000 to 4×10⁴ Å isat most 0.5 cc/g, and that of pores having a pore radius of 100 to 1000Å is at most 1.2 cc/g.

The composite oxide of this invention is agglomerated particles formedby agglomerating single ultimate particles having a particle size of 8to 50 rim, said agglomerated particles having a particle size of 1 to500 μm and an average particle size of 10 to 25 micrometers measured ina state of a slurry dispersed in water. A specific surface area of thecomposite oxide of this invention is usually 100 to 300 m² /g.

Moreover, pH of the dispersion obtained by dispersing the compositeoxide of this invention in water is 5 to 7 and nearly neutral.Accordingly, the composite oxide of this invention little dissolves inwater.

The composite oxide of this invention can be produced by, e.g., aprocess which comprises a first reaction step of adding an acid aqueoussolution capable of forming a silicate by reaction with an alkalisilicate to 7 to 10% by weight, calculated as silica, of an alkalisilicate aqueous solution in the presence of a salt at 10 to 45° C. suchthat a neutralization ratio becomes 20 to 40%, and a second reactionstep of heating the reaction solution obtained in the above reaction ata temperature of 90° C. to a boiling point of the reaction solution andadding thereto an acid aqueous solution capable of forming a silicate byreaction with an alkali silicate ("an acid aqueous solution capable offorming a silicate by reaction with an alkali silicate" is hereinaftersimply called "an acid aqueous solution) such that pH of the reactionsolution becomes 3 to 5.

In the first step of the above process, the acid aqueous solution isadded to 7 to 10% by weight, calculated as silica, of an alkali silicateaqueous solution at 10 to 45° C. such that a neutralization ratiobecomes 20 to 40%.

As the alkali silicate, sodium silicate is ordinarily used. Theconcentration of the alkali silicate aqueous solution is adjusted to 7to 10% by weight, preferably 8 to 9% by weight, calculated as silica.When the concentration of the alkali silicate aqueous solution isdeviated from the above range, the pore volume of the resultingcomposite oxide becomes small, making it impossible to obtain thecomposite oxide of this invention.

As the acid aqueous solution which is added to the alkali silicateaqueous solution, a known acid aqueous solution corresponding to theoxide represented by the above formula is used without limitation.Examples thereof are aluminum sulfate and titanium sulfate. The acidaqueous solution is not particularly limited. Generally, an amount of ametal ion is 2 to 7% by weight calculated as an oxide, and an amount ofan acid is 10 to 30 weight/volume %, preferably 15 to 25 weight/volume%. It is especially preferable that the amount of an A1 ion is 2 to 5%by weight, calculated as Al₂ O₃ and the amount of a Ti ion is 4 to 7% byweight, calculated as TiO₂.

It is also possible to use a mineral acid conjointly with the acidaqueous solution. Any known mineral acid will do. Concrete examples ofthe mineral acid are hydrochloric acid, sulfuric acid and nitric acid.Sulfuric acid is commonly used. The concentration of the mineral acid isnot particularly limited, and may be selected from the range of 10 to 30weight/volume

The acid aqueous solution is added to the alkali silicate aqueoussolution such that the neutralization ratio becomes 20 to 40%.

In the present specification and claims, when the amount of the acidaqueous solution required to neutralize the overall amount of the alkalisilicate aqueous solution is rated at 100%, the neutralization ratioshows a ratio of the acid aqueous solution used therein.

When the neutralization ratio is lower than 20%, the single ultimateparticles become large to weaken agglomeration of the particles and apore volume of pores having a pore radius of 10⁴ Å or less is decreased,making it hard to obtain the composite oxide of this invention havingthe pope volume within the specific range. When the neutralization ratioexceeds 40%, agglomeration of the particles becomes strong, and the popevolume of pores having a pope radius of 10⁴ Å or less is decreased;especially, the pore volume of popes having a pore radius of 300 to4×10⁴ Å becomes less than 0.6 cc/g.

In order to obtain a composite oxide excellent in absorbability of inkand effect of preventing opacity of the paper after printing when usedas a paper-making filler, it is advisable that the neutralization ratiois within the range of 23 to 35%.

In the process for producing the composite oxide, the reaction of thefirst step is carried out at 10° to 45° C. That is, when the reactiontemperature is deviated from the above range, the pore volume of poreshaving the pre radius of 10⁴ Å or less is decreased, making it hard toobtain the composite oxide of this invention having the pore volumewithin the specific range.

Next, in the second step of the process for producing the compositeoxide, the reaction solution obtained in the first step is heated at atemperature of 90° C. to a boiling point of the reaction solution,preferably, 95° C. to the boiling point of the reaction solution. Whenthe temperature of the reaction solution is deviated from the aboverange, the pore volume of pores having the pore radius of 10 or less isdecreased, and the composite oxide of this invention having such a porevolume within the specific range can hardly be obtained. The pore volumeof 3,000 to 4×10⁴ Å is also decreased.

In the second step, after heating, the reaction solution is desirablyleft to stand at the heating temperature (so-called ageing) because itallows strong bonding of the agglomerated particles of the resultingcomposite oxide and increases the pore volumes occupied by the intendedspecific pores. The ageing time is not particularly limited, but mayusually be selected from the range of 10 to 30 minutes.

In the second step, the acid aqueous solution is added such that pH ofthe reaction solution becomes 3 to 5. When pH of the reaction solutionexceeds 5, formation of components of the composite oxide becomesinsufficient, and the pore volume of pores having the pore radius of 10⁴Å or less is decreased, making it difficult to obtain the compositeoxide of this invention having such a pore volume within the specificrange. Even when pH of the reaction solution is less than 3, it does notgreatly influence the pore volume of the resulting composite oxide, butprevents decrease in the amount of the alumina component of thecomposite oxide. For this reason, it is advisable that pH is 3 or more,preferably 4 or more.

It is desirous to gradually add the acid aqueous solution. Usually, anecessary amount of the acid aqueous solution is added over a period of60 to 120 minutes either continuously or intermittently.

In the process for producing the composite oxide of this invention, itis desirable to conduct the neutralization reaction of the first stepand/or the second step in the presence of a salt for increasing the porevolume occupied by the intended specific pores. As the salt, knownwater-soluble inorganic salts can be employed without limitation.Generally, water-soluble inorganic salts having a nucleating activity ispreferably adopted. Concrete examples thereof are alkali metal saltssuch as sodium chloride, sodium sulfate, sodium nitrate, potassiumchloride, potassium sulfate and potassium nitrate. Although the amountof the salt is not particularly limited, it is usually selected from 0.5to 5% by weight calculated as an oxide in an alkali silicate aqueoussolution. It is advisable to add the salt to the reaction solutionbefore adding the acid aqueous solution because the pore distribution isgood and the given pore volume is less decreased even in milling of thecomposite oxide in the slurry state which is conducted as required.

The composite oxide of this invention is, when used as a paper-makingfiller, generally a filler dispersed in a starting pulp of a paper; itcan also be used as a paper coating.

When the composite oxide of this invention is used as a paper-makingfiller, a paper can be made by, after formation of the composite oxide,removing extra salt by means of filtration washing, etc., storing theresidue in a state of slurry dispersed in water, conducting milling andclassification, and mixing the resulting product in a slurry state assuch with a starting pulp. It is of course possible that the compositeoxide formed by the above process is dried, then stored as a powder,redispersed in water when mixed with the starting pulp and used.Although the amount of the composite oxide blended with the pulp fibersis not particularly limited, the composite oxide of this invention ispresent with the cumulative specific pore volume of pores having thespecific pore radius, with the result that the effect of preventingopacity of the paper after printing can be exhibited enough with itssmall amount. Accordingly, it is usually 0.1 to 2% by weight, preferably0.3 to 1.5% by weight.

In the composite oxide of this invention, the pore volume of poreshaving the pore radius of 10⁴ Å or less is very large. The compositeoxide of this invention therefore exhibits excellent absorption of ink.Especially, the composite oxide wherein the pore volume of pores havingthe pore radius of 5×10⁴ Å or less is 2.4 to 4.0 cc/g, that of poreshaving the pore radius of 3000 to 4×10⁴ Å is 0.6 cc/g or more and thatof pores having the pore radius of 100 to 1000 Å is 0.6 cc/g or more,when used as a paper-making filler, quite high in effect of preventingopacity of the paper after printing, which is greatly effective formaking the paper lightweight.

This invention is illustrated more specifically by referring to thefollowing Examples and Comparative Examples, but is not limited thereto.

BRIEF DESCRIPTION OF THE DRAWINGS

In the attached drawings, FIGS. 1, 2, 3 nd 4 show respectively graphsshowing results of measuring pore distributions of composite oxides inExamples 1 and 2 and Comparative Examples 1 and 2.

By the way, various properties in this invention were measured by thefollowing methods.

(1) Pore volume

100 ml of the reaction solution containing the composite oxide werefiltered with a Buchner funnel, and the composite oxide was washed with500 ml of water. The obtained cake was dried with a hot water drier at105° C. for 24 hours. A pore volume of the dried cake was then measuredthrough a mercury porosimeter. A cumulative graph showing a relationshipof a pore volume to a pore radius was prepared, and a pore volume in aspecific pore radius was found on the basis of said graph.

(2) Average particle size of particles after dispersed in water

It was measured by Coulter Multisizer (a trademark for a machinemanufactured by Coulter Electronics Inc.).

(3) pH

A reaction solution was sampled and pH was measured by a pH meter(manufactured by Horiba Seisaku-sho).

(4) Oil absorption

Oil absorption was measured according to JIS K5101.

(5) Chemical analysis

Chemical analysis was performed with a fluorescent X-ray analyzer(manufactured by Rigaku Denki K. K.).

(6) Paper-making test

As a pulp, a mixture comprising 10 parts by weight of NBKP (needle leafbleaching craft pulp), 45 parts by weight of TMP (thermomechanical pulp)and 45 parts by weight of DIP (dinking pulp) was stirred with a beaterfor 5 to 6 minutes, and 2% by weight, based on the dry pulp, of thecomposite oxide of this invention was then added, followed by stirringthe blend for 15 minutes. Subsequently, DH of the slurry was adjusted to4.5 with aluminum sulfate. Said slurry was then made into a paper by asquare sheet machine (300 mm×300 mm), and press-dehydrated. Theresulting wet paper was dried with a rotary dryer having a surfacetemperature of 110° C., and then seasoned at a relative humidity of 65%and a temperature of 25° C. for 24 hours to obtain a paper having abasic weight of 40 g/m² .

(7) Opacity of paper after printing

A solid print of 80×120 mm was applied to one side of a paper with acommercial printer (RICOH PRIPORT SS880: a trademark for a machinemanufactured by Ricoh Co., Ltd.), and opacity of paper after printingwas then measured. ##EQU1##

(8) Whiteness of paper

Whiteness of paper was measured according to JIS P8123.

(9) Opacity of paper

Opacity of paper was measured according to JIS P8138.

EXAMPLES 1 to 8

Commercial sodium silicate (SiO₂ 26.50 wt./vol. % by weight , SiO₂ /Na₂O molar ratio 3.04 ) , a sodium sulfate (Na₂ O 2.38 wt./vol. % byweight) and water were charged in a reaction vessel of an externalheating system such that a concentration calculated as silica shown inTable 1 were reached, and they were stirred.

In the first step, an acid aqueous solution of a type shown in Table 1was charged such that a temperature of a reaction solution and aneutralization ratio shown in Table 1 were reached. Subsequently, in thesecond step, the temperature was elevated to a temperature shown inTable 1, and stirring was then conducted in that state for a time shownin Table 1. The acid aqueous solution was then chalked over a course of100 minutes such that pH of the reaction solution became a value shownin Table 1 to terminate the reaction.

After the reaction solution was filtered, the cake was washed with waterand redispersed in water such that the solids content became 13 to 14%.600 ml of the dispersion were charged in a 2-liter polyethylenecontainer, milled together with 1 kg of glass beads having a size of 2mm at 420 rpm for 5 minutes and screened through a 145-mesh sieve. Aparticle size distribution of the solids content in the dispersion underthe sieve was measured.

Thereafter, the dispersion was filtered, and the cake was washed withwater and dried to obtain a composite oxide.

A chemical composition of the obtained composite oxide was measured, andits pore size distribution was measured with a mercury porosimeter. Thepore volume was calculated for each given pore radius. Moreover, acrystal structure was confirmed by X-ray diffraction, an averageparticle size in a slurry state, pH and oil absorption were measured,and a test of opacity after printing was run.

The results are shown in Table 2.

Incidentally, in a paper-making test, the composite oxide obtained inthe above reaction was directly made into a paper without separationfrom the dispersion and drying.

The results of measuring the pore distribution of the composite oxidesin Examples 1 and 2 are shown in FIGS. 1 and 2. In the drawings, (A) isa curve showing a cumulative specific pore volume of pores, and (B) is adifferential curve (dV/dlog R wherein V is a pore volume and R is a poreradius).

COMPARATIVE EXAMPLES 1 AND 2

The same measurements and test as in Examples 1 and 2 were carried outfor the composite oxides A and B shown in Table 1 (Comparative Examples1 and 2) which are commercially available. The results are shown inTable 2.

COMPARATIVE EXAMPLES 3 AND 4

Composite oxides were prepared in the same way as in Example 1 exceptthat the production conditions were changed as shown in ComparativeExamples 3 and 4 of Table 1.

The resulting composite oxides were measured and tested as in Example 1.The results are shown in Table 2.

                                      TABLE 1                                     __________________________________________________________________________           Alkali silicate aqueous                                                       solution (wt. %)                                                              Concen-                                                                            Concen-                                                                             1st step                                                           tration of                                                                         tration                Reaction                                                                           Neutral-                                     a sodium                                                                           calculated                                                                          Type of an acid, aqueous                                                                       temper-                                                                            ization                                      sulfate                                                                            as silica                                                                           solution         ature                                                                              ratio                                 __________________________________________________________________________    Example 1                                                                            1    8     Aluminum sulfate aqueous solution                                                              30   25                                                      (sulfuric acid 23 wt./vol. %                                                  Al.sub.2 O.sub.3 4 wt. %)                                   Example 2                                                                            1    8     Aluminum sulfate aqueous solution                                                              25   20                                                      (sulfuric acid 23 wt./vol. %                                                  Al.sub.2 O.sub.3 4 wt. %)                                   Example 3                                                                            1    7     Aluminum sulfate aqueous solution                                                              30   35                                                      (sulfuric acid 23 wt./vol. %                                                  Al.sub.2 O.sub.3 4 wt. %)                                   Example 4                                                                            1    7     Titanium sulfate aqueous solution                                                              35   30                                                      (sulfuric acid 25 wt./vol. %                                                  TiO.sub.3 6 wt. %)                                          Example 5                                                                            1    8     Aluminum sulfate aqueous solution                                                              30   20                                                      (sulfuric acid 23 wt./vol. %                                                  Al.sub.2 O.sub.3 4 wt. %)                                   Example 6                                                                            1    9     Aluminum sulfate aqueous solution                                                              35   30                                                      (sulfuric acid 23 wt./vol. %                                                  Al.sub.2 O.sub.3 4 wt. %)                                   Example 7                                                                            1    7     Aluminum sulfate aqueous solution                                                              30   35                                                      (sulfuric acid 23 wt./vol. %                                                  Al.sub.2 O.sub.3 2 wt. %)                                   Comparative                                                                          ZEOLEX 25 (Rhone Poulenc S.A.)                                         Example 1                                                                     Example 2                                                                            TIX-O-LEX 25 (Rhone Poulenc S.A.)                                      Example 3                                                                            1    6     Aluminum sulfate aqueous solution                                                              30   30                                                      (sulfuric acid 24 wt./vol. %                                                  Al.sub.2 O.sub.3 8 wt. %)                                   Example 4                                                                            1    8     Aluminum sulfate aqueous solution                                                              35   20                                                      (sulfuric acid 23 wt./vol. %                                                  Al.sub.2 O.sub.3 4 wt. %)                                   __________________________________________________________________________                   2nd step                                                                Ageing                  Reaction                                              time  Type of an acid, aqueous                                                                        temper-                                                                             pH after                                        (min.)                                                                              solution          ture (°C.)                                                                   reaction                               __________________________________________________________________________    Example 1                                                                              10    Aluminum sulfate aqueous solution                                                               95    3.9                                                   (sulfuric acid 23 wt./vol. %                                                  Al.sub.2 O.sub.3 4 wt. %)                                      Example 2                                                                              10    Aluminum sulfate aqueous solution                                                               95    3.1                                                   (sulfuric acid 23 wt./vol. %                                                  Al.sub.2 O.sub.3 4 wt. %)                                      Example 3                                                                              10    Aluminum sulfate aqueous solution                                                               95    4.1                                                   (sulfuric acid 23 wt./vol. %                                                  Al.sub.2 O.sub.3 4 wt. %)                                      Example 4                                                                              10    Aluminum silicate aqueous solution                                                              96    3.6                                                   (sulfuric acid 23 wt./vol. %                                                  Al.sub.2 O.sub.3 2 wt. %)                                      Example 5                                                                              10    Aluminum sulfate aqueous solution                                                               95    3.3                                                   (sulfuric acid 23 wt./vol. %                                                  Al.sub.2 O.sub.3 4 wt. %)                                      Example 6                                                                              10    Aluminum sulfate aqueous solution                                                               95    4.0                                                   (sulfuric acid 23 wt./vol. %                                                  Al.sub.2 O.sub.3 4 wt. %)                                      Example 7                                                                              10    Aluminum sulfate aqueous solution                                                               96    3.6                                                   (sulfuric acid 23 wt./vol. %                                                  Al.sub.2 O.sub.3 2 wt. %)                                      Comparative                                                                             ZEOLEX 25 (Rhone Poulenc S.A.)                                      Example 1                                                                     Example 2 TIX-O-LEX 25 (Rhone Poulenc S.A.)                                   Example 3                                                                              10    Aluminum sulfate aqueous solution                                                               95    3.6                                                   (sulfuric acid 22 wt./vol. %                                   Example 4                                                                              10    Aluminum sulfate aqueous solution                                                               85    3.3                                                   (sulfuric acid 22 wt./vol. %                                                  Al.sub.2 O.sub.3 4 wt. %)                                      __________________________________________________________________________

                                      TABLE 2                                     __________________________________________________________________________             iR.sub.2 O.jAl.sub.2 O.sub.3.kTiO.sub.2.mSiO.sub.2.nH.sub.2                                   Crystal                                                                             Pore volume (cc/g)                                      i  j  k  m  n   structure                                                                           1  2  3  4                                     __________________________________________________________________________    Example                                                                              1 0.68                                                                             1  0  20.6                                                                             0.25                                                                              amorphous                                                                           2.20                                                                             2.50                                                                             1.03                                                                             1.04                                         2 0.77                                                                             1  0  19.5                                                                             0.25                                                                              "     2.38                                                                             2.63                                                                             0.88                                                                             1.15                                         3 0.71                                                                             1  0  42.9                                                                             0.25                                                                              "     2.30                                                                             3.30                                                                             1.35                                                                             1.23                                         4 0.83                                                                             0.37                                                                             0.63                                                                             24.9                                                                             0.25                                                                              "     2.20                                                                             2.41                                                                             0.95                                                                             1.01                                         5 0.97                                                                             1  0  12.3                                                                             0.25                                                                              "     2.10                                                                             2.20                                                                             0.81                                                                             0.96                                         6 0.95                                                                             1  0  19.1                                                                             0.25                                                                              "     2.29                                                                             2.41                                                                             0.87                                                                             0.95                                         7 0.39                                                                             1  0  62.4                                                                             0.25                                                                              "     2.93                                                                             3.64                                                                             1.57                                                                             1.52                                  Comparative                                                                            1.12                                                                             1  0  14.9                                                                             0.25                                                                              "     1.85                                                                             2.27                                                                             0.53                                                                             1.15                                  Example                                                                              1                                                                             2 1.14                                                                             1  0  15.8                                                                             0.25                                                                              "     1.90                                                                             2.30                                                                             0.48                                                                             1.11                                         3 0.96                                                                             1  0  28.3                                                                             0.25                                                                              "     1.67                                                                             1.74                                                                             0.33                                                                             1.09                                         4 0.77                                                                             1  0  19.5                                                                             0.25                                                                              "     1.70                                                                             1.81                                                                             0.21                                                                             1.12                                  __________________________________________________________________________                               Opacity                                                     Average Particle                                                                          Oil   after      Opacity                                          size indispersion                                                                         absorption                                                                          printing                                                                           Whiteness                                                                           of paper                                         in water (μm)                                                                       pH (ml/100 g)                                                                          (%)* **    ***                                     __________________________________________________________________________    Example                                                                              1 16       6.1                                                                              210   78.0 58    84.3                                           2 15       6.7                                                                              230   77.8 58    84.5                                           3 16       5.6                                                                              230   78.1 57    84.2                                           4 16       5.8                                                                              210   78.0 59    85.0                                           5 15       5.7                                                                              210   77.3 58    84.7                                           6 16       5.6                                                                              210   77.7 58    84.5                                           7 16       5.4                                                                              250   78.8 57    84.0                                    Comparative                                                                            13       10.3                                                                             170   74.0 58    84.7                                    Example                                                                              1                                                                             2 13       10.2                                                                             180   74.3 58    84.8                                           3 15       5.9                                                                              150   73.3 57    84.1                                           4 16       5.8                                                                              160   73.2 58    84.3                                    __________________________________________________________________________     (Note)                                                                        1, 2, 3 and 4 in Table 2 show the following items.                            1 Pore volume of pores having a pore radius of 10.sup.4 Å or less.        2 Pore volume of pores having a pore radius of 5 × 10.sup.4 Å o     less.                                                                          3 Pore volume of pores having a pore radius of 3000 -4 × 10.sup.4      Å.                                                                        4 Pore volume of pores having a pore radius of 100 -1000 Å.               *blank = 72.5%                                                                **blank = 54.0%                                                               ***blank = 82.2%                                                         

What we claimed is:
 1. A process for producing an amorphous compositeoxide with the formula iR₂ O.jAl₂ O₃.kTiO₂.mSiO₂.nH₂ O, wherein Rdenotes an alkali metal, i is 0.3 to 1, k is 0 to 0.9, j+k=1, m is 7 to70, and n is 0.2 to 0.4, said composite oxide having a cumulativespecific pore volume of 2.0 to 3.0 cc/g, with respect to pores having apore radius of 10⁴ angstroms or less, the process comprising the stepsof:a) reacting an aqueous acidic solution, which is capable of forming acomposite oxide by reaction with an alkali silicate, with an alkalisilicate aqueous solution that contains an alkali silicate concentrationof 7% to 10% by weight, calculated as silica, in the presence of a saltat a temperature of 10° C. to 45° C., such that the neutralization ratiobecomes 20% to 40%, and b) heating the reaction solution from step (a)at a temperature of from 90° C. to the solutions's boiling point andthen adding sufficient aqueous acidic solution, which is capable offorming a composite oxide by reaction with an alkali silicate, so thatthe pH of said reaction solution becomes 3 to 5.